“We have all witnessed the devastating effect that the politics of purity can have,” Bennett and Kessler wrote, making specific reference to the current divisions within the Republican Party.

One major contentious division within the Democratic Party is the construction of the Keystone XL pipeline. A recent Pew study shows that support for the pipeline is overwhelming among Republicans and moderate Democrats, but liberal Democrats are split on the issue.

“A split is growing in the Democratic Party, one that ought to rival the divisions on the right that the headlines trumpet,” the Wall Street Journal’s Kimberley A. Strassel wrote on Thursday. “(The environmental left) channeled their frustration into the fight against Keystone, warning that they'll turn their significant money and resources against Mr. Obama's party if the president approves more ‘dirty oil.’ ”

The problem, according to Bennet and Kessler, isn’t differing opinions. It’s those who wish to eradicate or punish party members with dissenting views.

“If we are to make progress in a divided Washington,” Bennett and Kessler wrote in Politico Magazine, “we simply must embrace a big tent for the Democratic Party.